Deep-sea fish break the mold with novel visual system

Two deep-sea fish species, Maurolicus muelleri and Maurolicus mucronatus from the Red Sea, that have hybrid photoreceptors in their eyes as larvae and adults. — CHUNG WEN-SUNG/Reuters

For more than a century, biology textbooks have stated that vision among vertebrates – people included – is built from two clearly defined cell types: rods for processing dim light and cones for bright light and colour.

New research involving deep-sea fish shows this tidy division is, in reality, not so tidy.